Mastering DVD Mastering
You can hear those disks a-spinning in more and more edit bays these days. The editting previously involved only magnetic recording media, but the advent of DVD disks – originally called "Digital Versatile Disks" but now more commonly dubbed "Digital Video Disks" – require an optical recording medium similar to that used for music CDs. This new media is cheaper to produce in mass quantities than VHS tapes, is more universally compatible with inexpensive playback systems, and offers the random -access feature of "links" between different information areas.
The first DVD format, which was introduced in 1993 by Nimbus Technology and Engineering, held two hours of MPEG-1 video and promised to challenge the popularity of half-inch analog videotape at least for playback. But by 1995, under the pressure of competition from cable, satellite and video-on-demand services, two competing digital video disk formats – the Super Density (SD) variety backed by Toshiba and the Multi Media Compact Disk (MMCD) supported by Philips and Sony – were threatening to choke off the fledgling consumer DVD market in a rehash of the Betamax-vs.-VHS wars.
A group of computer companies headed by IBM led the charge to find a compromise and in September, 1995 the DVD Consortium (now the DVD Forum) was formed, it currently has more than 220 members.
Today, the promise of releasing video productions on DVD is alluring. But as Oliver Peters, senior video editor at the full-service production and postproduction company, Century III, in Orlando, Fla., learned last year, mastering the complexities of producing an interactive DVD can make even digital video seem simple. Assigned to be the interactive designer/project manager for the DVD Group at Century III, Peters spent a large part of last year and the beginning of this one working on a six-figure corporate marketing DVD entitled "The Power Behind the Scenes" for Evans & Sutherland of Salt lake City.
E & S is one of the originators of computer animation and computer-aided simulations, and the goal of this project was to provide a comprehensive overview of the many products and services the company offers worldwide.
"The DVD authoring spec is pretty convoluted," Peters said, "and we hit a lot of brick walls in the authoring process, requiring some inventive workarounds. You would think DVD files are as simple as menus and assets, but it is much more involved. There are about half a dozen different types of files you can create and they each have their own properties and limitations."
This was a pretty involved project with 136 video assets, including files for products, menus, transitions and approximately 1,500 interactive links. Debra Walker, director of marketing, and Video Producer/Director Ray Balhorn at E & S set the criteria that a viewer should be able to navigate between any two points on the DVD with only a couple of jumps.
The linear length of the final media was about 2 1/2 to 3 hours of video. It ended up on a single-sided, dual-layer format called DVD-9 and used up 7 GB of the disk’s potential 8.5 GB capacity.
The overall approach for the DVD was to have a human navigator (played by actor Chris Hurt) set the viewer on a path through any order of 70 video vignettes by guiding them along various information branches. The source material was all shot on Beta SP or DigiBeta by E & S or HDCAM by Century III. Editing those segments in standard definition on an Avid Media Composer, that part was fairly conventional. But then the fun began.
"To give all the segments a consistent look," Peters said, "we decided to nest them all in a 16:9 window inside an animated silver-metallic frame created in Photoshop and After Effects. That gave us room at the bottom of the screen for four button links that were common to every video section. If the viewer selected the button for the main menu selection, the camera rotated around a 3D cube on which the four options were represented until it settled on the menu choices for the desired video path. Even though the basic cube environment was created in Alias|Wavefront’s Maya by graphic specialist Scott Adams, by the time we had added titles and put each segment together in our Avid Symphony we actually had up to 45 individual animated elements that made up the menus in the video transition," Peters said.
The trick was to add the links that make a DVD so flexible. In reality, a DVD is actually just playing back a series of data files. The problem was that when the video makes a transition from one section to another, a DVD has to buffer the end of the previous file before it moves to the subsequent one. This requires about a half-second pause, and the audio – which is in a separate file – has to follow the video.
On top of keeping all that in sync, the looped animation effects and on-screen menus have to follow suit, so Peters had to plan the beginning and end of each segment to let the image effectively match-frame back to the beginning of the loop to prevent visible jumps.
Much time was spent at the front end to prevent the need for significant changes in the final phases.
CHOOSING A BIT-RATE
Taking this to the DVD format involves encoding the video into, in this case, MPEG-2, onto the encoding system’s hard drive. "Our first decision was to choose the bit-rate at which to encode the video and audio," Peters explained. "A typical movie on a DVD is 5.5 to 6 Mbps. At a higher bit-rate you get a better picture, but we learned that above 6 Mbps., we had trouble playing test disks on a laptop computer and the audio sync started to slip."
Then they moved to the DVD authoring phase to create the links between the raw files with the help of Century III’s compressionists Jeff Heisey and Nelson Hernandez. Here Peter learned a very important tip. "Create a very detailed flowchart right from the beginning," he recommends. "Typically you have a type of file module that you use for menus called Video Managers, and you need an intricate cross-reference between your links and files or data management can become very messy."
To verify their progress, Peters wanted to create a check disk on Century III’s one-off DVD burner. But he discovered that because all he could create in-house was a single-sided disk, he could not fully test whether all the random-access files would link properly when the viewer jumped from one layer to the other of the final double-sided DVD 9 format.
Evans & Sutherland had contracted with Future Media of Valencia, Calif., to replicate the project, but before the company could begin mass production the encoded data had to be recorded onto DLT tape to be sent to the West Coast. But they knew from the beginning that as complex a project as this one would have to be budgeted for multiple check disks.
"Creating a corporate DVD with as many interactive links as this one was a learning experience," Peters sums up. "When we started I didn’t realize how significantly individual software players on a computer would affect the look of our DVD excursion. And playing it back on a laptop computer, which is what the E & S sales team was looking for, proved that each brand handles the display in its own unique way."
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